Long-term coal chemical looping gasification using a bimetallic oxygen carrier of natural hematite and copper ore

Abstract Coal chemical looping gasification (CCLG) is a promising gasification technology for coal utilization with high resource utilization rate, energy saving and environmental protection properties. Development of suitable oxygen carriers and optimization of operating conditions for CCLG are the key for the coal conversion and H2&CO production (H2, CO). In this study, Cu-Fe bi-ore oxygen carrier prepared by spray drying granulation method using hematite and copper ore as raw materials was tested for CCLG. The effects of the reaction temperature, oxygen carrier to coal (O/L) ratio and steam addition amounts were systematically evaluated by reaction tests combing with various analytical methods. Most importantly, over 100 redox chemical looping cycles were performed to demonstrate the excellent stability of Cu-Fe bi-ore oxygen carrier during the redox reactions. Results showed that the optimal gasification condition is 950 °C with oxygen carrier-to-coal mass ratio of 3:1 and steam rate of 0.08 ml/min. Syngas yield of 58 mmol/g, as well as 75.2% syngas selectivity and 85.3% carbon conversion were achieved. After 100 redox cycles, the synthesis gas yield can still reach 46 mmol/g despite a decline, and the carbon conversion kept above 72%, without obvious sintering in the long-term test. The characterization results showed that the synergistic effect between Cu and Fe metals contributed to its good oxygen release ability and reducibility. The Cu-Fe bi-ore oxygen carrier undergoes a gradual reduction Fe3+→Fe8/3+→Fe2+→Fe and Cu2+→Cu process during the gasification reaction, accompanying with the lattice oxygen migration from bulk to the particle surface. This work demonstrated the economical method for the industrial application of CCLG process using spray-drying-derived oxygen carriers.